Bone cement plugs are well known in the art. Such devices are generally used in conjunction with bone cement dispensers to compact bone cement into a bone canal before fixing a prosthetic device in that bone canal. By way of example, bone cement plugs are commonly used in conjunction with bone cement dispensers to compact bone cement into the intramedullary canal of the femur before fixing the femoral stem of an artificial hip in that canal.
More particularly, in total joint replacement surgeries, such as hip and shoulder replacements, bone cement is commonly used to fix the stems of the prosthetic devices into the medullary canals of the joint's bones. In this respect, it has generally been found that a prosthetic device will be more securely fixed in a bone canal if the bone cement is well packed into the bone canal before the stem of the prosthetic device is positioned in the bone canal.
To this end, after initial preparation and cleaning of the bone canal, the distal portion of the canal is generally occluded with a plug. The bone cement plug serves to limit uncontrolled flow of bone cement into the distal portion of the bone canal. Ideally, the bone cement plug limits the column of bone cement to about 1 to 2 cm beyond the distal tip of the stem of the prosthesis. After the plug has been set at the distal portion of the bone canal, the bone cement is injected into the distal-most part of the occluded bone canal, adjacent to the plug, using a bone cement dispenser having a long nozzle. The bone canal is then filled with bone cement in a retrograde fashion, by withdrawing the nozzle of the bone cement dispenser from the distal end of the bone canal to the proximal end of the bone canal, as the cement issues from the nozzle. Such retrograde filling helps avoid trapping air in the distal-most part of the bone canal.
After the bone canal has been filled with bone cement, a bone canal pressurizer is then connected to the bone cement dispenser. The pressurizer is pressed against the open end of the bone so as to occlude the proximal end of the bone canal. More cement is then injected into the bone canal through the pressurizer and under pressure. Under such pressurization, the cement in the bone canal intrudes into the interstices of the inner surface of the bone wall defining the bone canal. When the bone cement thereafter sets, a micro-interlock is established between the cement and the irregularities of the inner surface of the bone wall. This significantly enhances fixation of the prosthetic device in the bone canal.
Ideally, a bone cement plug should be easy to deploy at the desired depth in the bone canal, effective in closing off that bone canal and, in the event that the bone cement plug subsequently needs to be removed, easy to retrieve from the distal end of the bone canal. The bone cement plug must also be bio-compatible with the patient. Furthermore, the bone cement plug should be inexpensive to produce.
A variety of bone cement plugs are known in the art.
See, for example, the bone cement plugs described and illustrated in U.S. Pat. Nos. 4,245,359; 4,276,659; 4,293,962; 4,302,855; 4,344,190; 4,447,915; 4,627,434; 4,686,973; 4,697,584; 4,745,914; 4,936,859; 4,950,295; 4,994,085; 5,061,287; 5,078,746; 5,092,891; 5,376,120; and 5,383,932.
See also, for example, the bone cement plug described and illustrated in British Patent Document No. 2,253,564A.
See also, for example, the publication entitled "Polyethylene medullary plug according to Stuhmer/Weber" distributed by ALLO PRO AG of Switzerland.
See also related apparatus described and illustrated in U.S. Pat. Nos. 4,011,602; 4,523,587; and 4,904,267.
See also related apparatus described and illustrated in European Patent Document No. 0,006,408 B1; and PCT Patent Document No. WO 94/15544.
Unfortunately, however, all of the bone cement plugs developed to date tend to suffer from one or more significant disadvantages.
More particularly, in general, the fixation of the bone cement plug depends on the friction established between the wall of the bone canal and the bone cement plug. Currently, the most common surgical technique is to first measure the size of the prepared bone canal. This typically involves sequentially inserting a number of "sizers" into the bone canal so as to determine the gross cross-sectional diameter of the canal at the desired depth. Having thus determined the size of the bone canal, an over-sized plug is then inserted into the canal so as to occlude the bone canal at the desired depth.
Unfortunately, however, if the bone cement plug is not sufficiently over-sized relative to the diameter of the bone canal, or if the plug is too easily deformable, the bone cement plug's engagement with the wall of the bone canal will be less than optimal, and this may lead to complications. In particular, during the aforementioned pressurization phase, or during the subsequent insertion of the prosthesis, the increased pressure of the bone cement can cause the insufficiently-anchored plug to migrate distally. On the other hand, if the bone cement plug is too greatly over-sized, and/or if the plug is overly rigid, the bone cement plug cannot be inserted into the bone canal to the desired depth. Also, excessively forceful insertion of the bone cement plug into the bone canal can cause the wall of the bone canal to fracture in some circumstances.
In addition to the foregoing, many of the current bone cement plugs cannot be adequately anchored against the wall of the bone canal if the plug needs to be located distally of the isthmus, i.e., against a portion of the bone canal located distally of the narrowest part of the canal. This is because the largest possible size of the bone cement plug is limited by the need for the bone cement plug to pass through the narrowest part of the bone canal. In other words, in this situation, a smaller than desired plug size must be used.
Various expandable plugs have been designed to address the foregoing issues. However, such known expandable bone cement plugs suffer from a number of drawbacks, such as difficulty in manufacturing, inadequate fixation, the complexity of their associated insertion tools, etc.